This invention relates to pistons for internal combustion engines and more particularly to pistons and a method of making the same of forged aluminum with a fusion welded wear-resistant ferrous alloy crown insert.
The advantages of light weight pistons for internal combustion engines have been appreciated for a long time as shown in U.S. Pat. No. 1,727,119. Very early it was suggested that the pistons be made of aluminum whose defects of uneven expansion and poor hot-strength were recognized in the aforesaid U.S. Pat. No. 1,727,119. Also recognized was the feasibility of providing cast aluminum pistons with iron elements such as inserts and skirts to improve the wear and strength as shown in U.S. Pat. Nos. 1,717,916; 3,012,831; and 3,305,916. In the latter patent the aluminum piston is cast around a ring insert positioned in a mold and the interior of the piston is then formed by a forging operation.
The better mechanical and thermal properties of forged aluminum alloy pistons for meeting the requirements of internal combustion engines is recognized. However completely forged aluminum alloy pistons having ferrous metal ring inserts have not been successful due to the absence of an integral metal bond between the iron insert and the pre-forged piston. The previous method of making pistons with ring inserts, as shown in the mentioned prior art, required casting of the piston with the ring in place to form a metallic bonding between the ring insert and the cast piston body.
However, as mentioned, the joining of the iron insert to the pre-forged aluminum piston does not provide the required bonding.